In the field of microfabrication typified by production of integrated circuit devices, fine resist patterns have been conventionally formed by: forming a resist coating film on a substrate with a resin composition containing a polymer having an acid-dissociable group; irradiating the resist coating film through a mask pattern with a radioactive ray having a short wavelength such as an excimer laser to permit exposure; and removing light-exposed sites with an alkaline developer. In this process, a chemically amplified resist provided by including in a resin composition a radiation-sensitive acid generating agent that generates an acid upon irradiation with the radioactive ray to improve the sensitivity by the action of the acid has been used.
With respect to such a chemically amplified resist, as a method for forming still finer resist patterns having a line width of e.g., about 45 nm, utilization of a liquid immersion lithography process has been increasing. In this method, exposure is carried out in a state in which an exposure light path space (between a lens and a resist coating film) is filled with a liquid immersion medium having a greater refractive index (n) as compared with that of the air or an inert gas such as, for example, pure water, a fluorinated inert liquid, etc. Therefore, it is advantageous in that even if a numerical aperture (NA) of a lens is increased, the focal depth is less likely to decrease, and higher resolving ability can be achieved.
Demands for a resin composition used in a liquid immersion lithography process have included: suppression of elution of the acid generating agent and the like from the formed resist coating film to the liquid immersion medium, thereby preventing deterioration of performances of the coating film and prevention of contamination of the apparatus such as a lens; and improvement of water draining property of the surface of the resist coating film to prevent leftover of watermarks, thereby enabling exposure by high speed scanning. Although Japanese Unexamined Patent Application, Publication No. 2005-352384 has proposed a technique of forming an upper layer film (protective film) on a resist coating film as a means for accomplishing such demands, a film formation step is separately required making the operation complicated. Therefore, methods for enhancing the hydrophobicity of the surface of the resist coating film have been studied, and for example, PCT International Publication No. 2007/116664 has proposed a resin composition containing a highly hydrophobic fluorine-containing polymer.
However, when the hydrophobicity of a resist coating film is enhanced, surface wettability for a developer and a rinse liquid is deteriorated; therefore, removal of development residues deposited during development on the surface of the resist at sites unexposed with light may be insufficient, whereby development defects such as a blob may occur. For the purpose of preventing such development defects, Japanese Unexamined Patent Application, Publication No. 2010-032994 has proposed a fluorine-containing polymer that is hydrophobic during liquid immersion lithography but the hydrophobicity decreases upon development with an alkali, specifically, a fluorine-containing polymer that includes a carboxylic acid into which a fluoroalkyl group has been introduced.
In these documents, a change of hydrophobicity of the resist coating film was confirmed using a static contact angle for water as a marker. However, as a marker concerning the aforementioned water draining property which matters in practical liquid immersion lithography processes, a dynamic contact angle such as a receding contact angle rather than a static contact angle is believed to be more significant. In addition, for shortening of the time period of a development process, it is also desired to cause the change of the dynamic contact angle within a shorter period of time during a treatment with a developer. In this regard, a degree of a decrease in a dynamic contact angle after the development with an alkali of the fluorine-containing polymer, and a time period required for change in a contact angle indicated in the documents described above cannot sufficiently contribute to improvement in practical liquid immersion lithography processes.